1. Fields of the Invention
This invention relates to battery powered electric appliances, more particularly to portable type electric appliances powered by main and subsidiary batteries both incorporated therein.
2. Description of the Prior Art
A conventional portable type electric appliance such as an electric dry shaver is provided with a built-in battery for driving an electric motor, a vibrator, or other kind of electric loads. Such battery is required to be light in weight as well as small in size in order to make the electric appliance portable. Accordingly, the battery is not expected to have a larger capacity due to the restriction on its weight and size. This presents a problem that the battery is subject to a shorter operational life. When an electric dry shaver is powered by such battery of small capacity, for example, it is frequently seen that the operation is interrupted during the shaving by an user, which annoys the user. In order to obviate this drawback, a scheme is suggested as in U.S. Pat. No. 3,108,192 wherein a main battery and a reserve battery are selectively connected to a load by means of a switch. Namely, the reserve battery is to take the place of the main battery, when the main battery becomes empty while the electric appliance is in operation, preventing a sudden interruption of the operation of the electric appliance. However, this type has a drawback that the reserve battery will not take the place of the main battery, if the reserve battery has been already exhausted by mistake before the main battery becomes empty, which would be avoided if the reserve battery were arranged not to be used prior to the main battery.